[Samk15]

Hi,
I started to test the FR of my earphones and after running few tests I noticed that the recorded FRs for all earphones follow similar pattern.

There is a drop around 8K and I wonder if it's due to the type of coupler I'm using or something else?

Can someone shed some light into this?
Cheers.

 

[Samk15]

See the attached image.

 

[Samk15]

 

[GREQ]

It's common in all measurement rigs that there will be consistent anomalies such as this (at varying degrees).

With my miniDSP E.A.R.S. jig, the very same thing occurs almost consistently around 4-4.5kHz with closed-back headphone measurements (although my anomalous results are not so extreme as yours).
Only the very most expensive measurement systems are designed to prevent this.

For most users, this is normal and expected.
As long as you're aware that it exists, it's not a huge problem until you come across a headphone with a sharp peak at 8kHz.

 

[Samk15]

It's common in all measurement rigs that there will be consistent anomalies such as this (at varying degrees).

With my miniDSP E.A.R.S. jig, the very same thing occurs almost consistently around 4-4.5kHz with closed-back headphone measurements (although my anomalous results are not so extreme as yours).
Only the very most expensive measurement systems are designed to prevent this.

For most users, this is normal and expected.
As long as you're aware that it exists, it's not a huge problem until you come across a headphone with a sharp peak at 8kHz.

Thanks GREQ,

It's understandable but one of the earphones that i tested should exhibit a very flat FR whereas it follows this weird sort of FR algorithm as the other two earphones.

To make things further more complicated l. I ran a free air test of the mic in a reasonably silent environment. The results were unusual. (See the attached image)

I was expecting more flat results

 

[GREQ]

Without knowing what kind of set-up you're using it's difficult to know why you might be getting these results.
However, I would guess it seems to be an issue with the coupling method used between the microphone/jig and headphone.

 

[surfgeorge]

Using a simple IEM measurement microphone and coupler is a great way to compare IEMs, specifically if you do some modifications to them.
I am using the Dyton IMM-6 mic with some 3D printed couplers and I experimented with trying to 3D print a IEC711 like coupler.
In the end I got the best results with a simple coupling tube.

I can only recommend to experiment with the length of the tube until your measurements resemble reference measurements most closely and take this as your baseline.
With that you can then measure your IEMs and look at the differences.

I found that quite helpful to learn about FR and perceived sound characteristics, and to learn about the limitations of a frequency graph in judging the SQ of an IEM.

 

[castleofargh]

Thanks GREQ,

It's understandable but one of the earphones that i tested should exhibit a very flat FR whereas it follows this weird sort of FR algorithm as the other two earphones.

To make things further more complicated l. I ran a free air test of the mic in a reasonably silent environment. The results were unusual. (See the attached image)

I was expecting more flat results

This graph looks like pink noise or a log sweep, which would give that type of diving FR graph. It's not the problem you're asking about, but it won't hurt to use a proper test signal.

As for the 8kHz thing of the previous graph, well the most reasonable way to look at it is to accept that high frequencies will be unreliable. This should be pretty obvious when looking up online graphs, but the reality is even worse because most people sharing their graphs online have first tried to copy some reference(usually another guy making online graphs who copied another guy who ...). So chances are that a lot of those online graphs are compensated in some ways to look less different than the RAW measurement actually are. You just have to pick your poison: 1. Leave the high freqs alone and only use FR graphs from your cheap rig for what they do right, comparisons between 2 IEMs you have measured yourself. AKA reasonable objective use of the data you have.
2. Also try to copy someone's response with a calibration curve, and if it even works in a consistent way(probably won't), make your target known so people have a chance to avoid misinterpreting stuff.

Just know that within what you can find online, some will like you have some recess somewhere near 8kHz, while some actually do all they can to place a resonance around there, so their graphs will show more 8kHz(or near that) than there would be in an expensive dummy head or probably in your own ears. Personally, on my measurement toy rig that I use and trust the most, I have a calibration file I made based mostly my personal hearing and a few other human hearing expectations based on research. And I stopped that calibration file at 8kHz ironically. Above, I've found things to vary too much depending on rather small variables(insertion, tips, coupler). Those differences only get bigger when compared to subjective impressions(2 people may judge an IEM in mostly similar ways in the low end and midrange, but they may describe up to 20dB differences between each other in the upper frequencies. So I've got up to where I thought I was still getting fairly consistent results, and above 8kHz on that rig, "que sera sera".

 

[Samk15]

I'm using imm6 and AudioTools app on my LG V30.

I put the imm6 in a relatively sealed box to minimize environmental noise and run averaging test for at least 3mins using both my LG V30 (below picture) and Asus Zenfone (top picture). No coupler was attached.

I noticed that the spl level starts around 40db and increases by 1db every 30-45 sec. Is this normal/expected?



As you can see from the screenshots, the mic records some noise that doesn't exist!

 

[Samk15]

After multiple tests using different type/size of couplers, I come to the conclusion that the imm6 is incapable of recording treble frequencies accurately beyond 6Khz.

I even connected the eartip directly to the mic without any coupler and it produced the same output (although with less bass).

Watch the below short clip for comparison:



So imm-6 is only good to record vocals! and cannot be used for FR measurement.